As a radiation treatment method used in a case where a patient's affected area moves due to respirations, cardiac beats, and intestinal movements, an ambush irradiation method and a pursuing irradiation method are known.
In these irradiation methods, a patient's internal body is periodically imaged with perspective X-rays to periodically generate a perspective image containing an image of a patient's affected area or a marker indwelled around the affected area. Then, matching with a template is performed to track the affected area or the marker, and the affected area is irradiated with treatment beams. The template is registered, by users such as medical doctors and radiation technologists, in a perspective image for preparing a template. The perspective image for preparing a template is generated through previous imaging of the patient's internal body with perspective X-rays during, for example, treatment planning.
Alternatively, background differencing technique is performed on a perspective image that is periodically imaged during treatment to track a marker, and then, an affected area is irradiated with treatment beams.
In the method where a user registers the image of an affected area or a marker in a perspective image for preparing a template to the template, like the known techniques described above, for registering the template, a subject needs to be irradiated with perspective radiation to generate the perspective image for preparing a template. Accordingly, the exposure dose of the subject comes to be increased.
Especially, for addressing a problem that an image of the affected area and a marker in a perspective image varies in shape depending on the position of the affected area or the marker in the subject, a plurality of template perspective images are imaged at different times to register the image of the affected area and the marker in each template perspective image to the template. In such a case, the exposure dose of the subject comes to be further increased.
Furthermore, in the method of performing background differencing technique on the perspective image imaged during treatment thereby to detect the image of the marker, irradiation with perspective radiation needs to be strengthened so as to inhibit erroneous detection of noises contained in the perspective image. Accordingly, the exposure dose of the subject comes to be increased. It is noted that the affected area itself is difficult to be detected by the background differencing technique.